In recent years, a machining method, called a remote laser machining method, has been drawing attention. In the remote laser machining method, laser welding is performed by radiating a laser beam from a position away from a machining point to the machining point, using a laser beam having a long focal length. Generally, the laser machining head used for the remote laser machining has a condensing lens in the upper part and has a nozzle unit fitted at the tip in the lower part. The laser beam introduced to the laser machining head is condensed by the condensing lens, goes through the inside of the laser machining head, and is finally radiated from the nozzle unit to a workpiece. In accordance with the radiation of the laser beam, the laser machining head cuts a workpiece by jetting assist gas from the nozzle unit and blowing the melt of the workpiece.
In such a laser machining head, the laser beam goes through the condensing lens in laser machining, thus the temperature of the condensing lens increases. For this reason, in order to prevent deformation of the condensing lens caused by the temperature increase, a so-called thermal lens phenomenon, a method for cooling the condensing lens with assist gas is proposed. For instance, Patent Literature 1 describes a laser machining head that has a gas path in the holder on the periphery of the lens and lens receiver and cools the lens with assist gas going through the gas path.
In such a laser machining head, spatter and dust generated in laser machining can adhere to the condensing lens. Thus, a method for preventing adhesion of spatter and dust to the condensing lens using the assist gas is proposed. For instance, Patent Literature 2 describes a laser machining head in which adhesion of spatter and dust to the condensing lens is prevented by blowing an assist gas flow onto the surface of the condensing lens.
With reference to FIG. 6, a specific description is provided. FIG. 6 is a drawing showing laser machining head 900 of the conventional laser machining apparatus. As shown in FIG. 6, conventional laser machining lead 900 includes lens holder 901, condensing lens 902, lens receiver 903, lens retainer 904, guide ring 905, sleeve 906, nozzle holder 907, and nozzle 908. Condensing lens 902 is held in lens holder 901 via lens receiver 903 and lens retainer 904. Lens holder 901 has gas introduction hole 909 on the side face. Under lens holder 901, guide ring 905 is fixed. Further, sleeve 906, nozzle holder 907, and nozzle 908 are disposed under guide ring 905.
Along the outer peripheral edge of the top end of guide ring 905 of laser machining head 900, inclined guide surface 910 is disposed. Along the inner peripheral edge of the tip of lens retainer 904, inclined guide surface 911 is disposed. The assist gas introduced from gas introduction port 909 is blown onto condensing lens 902 by inclined guide surfaces 910, 911, and is finally jetted to workpiece W from nozzle 908.